This invention relates to polyurethane (PU) foam made from lipid-based polyols, and in particular to flexible PU foam although rigid, semi-flexible/semi-rigid and microcellular foams are also envisaged.
Methods for the manufacture of polyurethane foams (eg flexible PU foams) are known in the art and are covered, for example, on pages 170-235 of the Plastics Manual, Volume 7, Polyurethanes, Becker/Braun, 2nd edition, published by Carl Hanser Verlag.
Conventionally, PU foam (eg flexible, semi flexible and rigid PU foams) may be made by reacting a polyol with a multifunctional isocyanate so that NCO and OH groups form urethane linkages by an addition reaction, and the polyurethane is normally foamed with carbon dioxide produced in situ by reaction of isocyanate with water, although other volatile non reactive solvents and gases e.g acetone, pentane and injected carbon dioxide and mechanical frothing may be used to form the cell spaces within the foam.
This conventional process may be carried out as a so-called ‘one-shot’ process whereby the polyol, isocyanate and water and/or solvent are mixed together with catalysts and other additives so that the polyurethane is formed and foamed in the same step. The process may be carried out under conditions of increased or reduced atmosphere pressure so as to effect the density and other characteristics of the final product.
It is however also known to use a two step process whereby in a first step polyol is reacted with isocyanate to give a so-called ‘isocyanate modified polyol’ and this is foamed, by reaction of isocyanate and water, with or without inert solvent and or gases, to produce carbon dioxide, in a second step.
It is desirable to make Urethane foams (microcellular, rigid, semi flexible/semi rigid and flexible) from lipid-based polyols such as natural oil based polyols (NOPs). At the moment, at the date of this application, there are limits to the maximum level of incorporation of NOPs into urethane formulations, for example in one of the biggest potential uses for NOPs, in the so called conventional flexible slabstock foam market, a maximum of only approximately 22 percent (php) of the crude oil based polyol can be replaced by an NOP. Higher incorporation level than this may be theoretically possible but even by 30 php in conventional flexible foams, the materials do not have good enough physical properties (such as good compression set, low foam settle after full rise, good foam processing and processing safety, good foam stability, good hand touch including resilience and ball rebound, good SAG (support factor), good flammability, low hysteresis loss and good foam hardness) to be useable by most customers. In HR (High Resilient) foam formulations the tolerated limit of inclusion of NOPs can be as low as 5 php but is typically about 10 php. Above the levels discussed generally here, unacceptable faults, for example, internal faults or “splits”, also pockets of collapsed foam may appear in the material and this can be a visual sign that instability may be about to occur leading to the material being a loss or fit only for scrap. The limited inclusion of NOPs is seen for instance in examples in Renosol WO 2009/026424.
The incorporation of these NOP materials into Urethane formulations is complex for two major reasons. The first is that NOPs, by their very structures, are hydrophobic as the chains do not contain oxygen linkages (ether or ester) compared to standard petroleum based Urethane raw materials. As such they do not readily mix and therefore do not readily react with other components also present in the formulation, which have been developed prior to the introduction of NOPs.
The second problem is that in NOPs the OH groups are generated by utilization of double bonds, transesterification with multifunctional alcohols or radical cleavage/oxidation. All of these tend to give sterically hindered hydroxyl groups, distributed at specific points along the carbon chain of the natural oil, as opposed to being placed at the end of the chain which is the case for standard petrochemical (crude oil) derived polyols. The NOP's hydroxyl groups are naturally therefore of lower reactivity than conventional (or alkyleneoxy) based polyols.
The smell of foams containing natural oil-based polyols can also be a problem, since an odour of “French Fries” or “Freedom Fries” (hot cooking oil) has been noted. This odour is thought to be the result of the presence of such materials as, but not restricted to, hexanal, nonanal, decanal and other aldehydes, and/or ketones and carboxylic acids and other derivatives, in or originating from the original natural oil-based polyol production process, and would preferably be avoided, minimised or removed. The odour effect of these and other odour materials is lessened or eliminated during the stage at which the natural oil-based polyol is transformed into the isocyanate modified polyol in a “pre treatment” according to the present invention.